This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
In wireless communications networks, an access node's UL and Downlink (DL) service areas are closely related to the condition for updating cell lists of terminal devices in proximity of the access node and the condition for changing serving access nodes of the terminal devices. In UL, a terminal device transmits to the access nodes associated with all cells in its cell list. In DL, the terminal device receives from its serving access node.
According to the prior art, in determining whether the condition for updating the cell lists of the terminal devices and the condition for changing their serving access nodes are met, a set of Cell Individual Offsets (CIOs) configured for a set of cells are considered.
To be specific, the condition for updating the cell list of a terminal device may include a condition for adding a cell to the cell list and a condition for removing a cell from the cell list, which may be expressed as the following formulas (1) and (2) respectively. The condition for changing the serving access node of the terminal device may be expressed as the following formula (3).qualityCPICHnew+CIOnew>qualityCPICHbest+CIObest−addhysteresis  (1)qualityCPICHnotest+CIOnotbest<qualityCPICHbest+CIObest−removehysteresis  (2)qualityCPICHnotest+CIOnotbest>qualityCPICHbest+CIObest−switchhysteresis  (3)
where
qualityCPICHnew, qualityCPICHnotbest and qualityCPICHbest respectively denote a quality measurement for a cell not included in the cell list, a quality measurement for a non-best cell in the cell list and a quality measurement for a best cell in the cell list;
CIOfirstnew, CIOfirstnotbest and CIOfirstbest respectively denote one of the set of CIOs which corresponds to the cell not included in the cell list, one of the set of CIOs which corresponds to the non-best cell in the cell list and one of the set of CIOs which corresponds to the best cell in the cell list; and
addhysteresis, removehysteresis and switchhysteresis respectively denote a hysteresis value delaying the addition of the cell, a hysteresis value delaying the removal of the cell and a hysteresis value delaying the changing of the serving access node.
In certain scenarios, it might be preferable to manipulate the access node's UL service area. By way of illustration rather than limitation, it is preferable for a Low Power Node (LPN) in a heterogeneous network to extend its UL service area.
To illustrate this, FIG. 1 depicts a heterogeneous network comprising a macro base station and several Low Power Nodes (LPNs), each of which may be a Remote Radio Unit (RRU), a pico base station, a micro base stations or the like. Typically, because the transmission power of the macro base station (e.g., 20 W) is much higher than that of the LPN (e.g., 2 W), an inherent macro-LPN imbalance region exists as illustrated in FIG. 2. In that region which is determined by a first border at which the pathloss with respect to the macro base station is equal to the pathloss with respect to the LPN and a second border at which the DL reception power from the macro base station is equal to the DL reception power from the LPN, the UL transmission quality to the LPN is better than the UL transmission quality to the macro base station while the DL transmission quality from the macro base station is better than the DL transmission quality from the LPN.
In DL, terminal devices located in the imbalance region are served solely by the macro base station (i.e., the terminal devices located in the imbalance region receive DL transmissions solely from the macro base station). Thus, the boundary between the DL service areas of the macro base station and the LPN corresponds to the second border of the imbalance region.
In UL, terminal devices located in a Soft Handover (SHO) region which overlaps with the imbalance region are jointly served by the macro base station and the LPN (i.e., the terminal devices located in the SHO region transmit UL transmissions to both the macro base station and the LPN). Thus, the boundary of the LPN's UL service area corresponds to one of the SHO region's two borders which falls into the imbalance region.
To benefit more from the higher quality UL transmissions provided by the LPN in the imbalance region, it is preferable to extend the UL service area of the LPN. To this end, one approach is to increase the CIO for the LPN, which according to the above formulas (1)-(3) is considered not only in determining whether the condition for updating the cell list of the terminal device in proximity of the LPN is met but also in determining whether the condition for changing the serving access node of the terminal device is met. Undesirably, increasing the LPN's CIO also extends the DL service area of the LPN into the macro-LPN imbalance region, and terminal devices located in the extended part of the LPN's DL service area can no longer benefit from the higher quality DL transmissions from the Marco base station.
Another approach for extending the LPN's UL service area is to enlarge the SHO region by increasing addhysteresis and/or removehysteresis in the above formulas (1) and (2). In addition to an extension of the LPN's UL service area, the enlargement of the SHO region leads to an extension of the macro base station's UL service area, causing increased processing cost. Moreover, the addition of the macro base station into the cell list might prevent the LPN from being added because the cell list might be full after the addition of the macro base station. Accordingly, it is still impossible to benefit from the higher equality UL transmissions provided by the LPN in the imbalance region.
From the perspective of the macro base station, the approach to contract the macro base station's UL service area by decreasing its CIO may undesirably cause the contraction of the macro base station' DL service area. The approach to contract the macro base station's UL service area by diminishing the SHO region may undesirably cause the contraction of the LPN's UL service area.